The present invention generally relates to zoom lens apparatuses, and more particularly to a zoom lens apparatus having a stable zooming performance.
A lens system of a televison camera is generally constituted by a focus lens group, a variable power lens group, a compensating lens group and a master lens group which are respectively arranged on an optical axis. The variable power lens group and the compensating lens group constitute a zoom lens system. Generally, in a telephoto mode, the variable power lens group and the compensating lens group are adjusted so that the two lens groups are positioned close to each other compared to the respective positions in a standard mode. On the other hand, in a wide angle mode, the variable power lens group and the compensating lens group are adjusted so that the two lens groups are positioned apart from each other compared to the respective positions in the standard mode.
As will be described later on in the specification in conjunction with drawings, a conventional zoom lens apparatus comprises a first frame for supporting the variable power lens group, a second frame for supporting the compensating lens group, guide rails for guiding the first and second frames, and a hollow cylindrical member for accommodating the first and second frames and the guide rails. The first and second frames have first and second projections, respectively, and first and second cam grooves for receiving the first and second projections are formed on a peripheral surface of the hollow cylindrical member. As the hollow cylindrical member is rotated, the first and second projections move along the corresponding first and second cam grooves. The first and second cam grooves are shaped so that the first and second frames close upon each other or separate from each other under the guidance of the guide rails when the hollow cylindrical member is rotated.
However, the conventional zoom lens apparatus has a problem in that the zooming performance of the the zoom lens apparatus (that is, the product) is inconsistent among the zoom lens apparatuses due to deviations in the dimensions of the hollow cylindrical member, the first and second projections, the first and second cam grooves, the thickness of the lenses and the like. In other words, when forming the parts which constitute the zoom lens apparatus, slight deviations or errors in the dimensions of the parts are inevitably introduced. For this reason, it is impossible to manufacture zoom lens apparatuses (products) having a stable zooming performance.